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Transcript of Oxxi iddaattioonn Cooff nAAllccoohho oll...
OOxxiiddaattiioonn ooff AAllccoohhooll CCoommppoonneenntt ooff MMiiccrrooeemmuullssiioonn bbyy
LLiippoopphhyylliicc CCrr((VVII))
AA DDiisssseerrttaattiioonn
SSuubbmmiitttteedd iinn Partial fulfillment
FOR THE DEGREE OF
MASTER OF SCIENCE IN CHEMISTRY
Under The Academic Autonomy
NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
By Santosh Kumar Behera
Roll No-409cy2006
Under the guidance of
Dr. Sabita Patel
Department of Chemistry
National Institute of Technology, Rourkela
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Dr. Sabita Patel
Asst. Professor
Department of Chemistry
National Institute of Technology
Rourkela-769008, India
CERTIFICATE
This is to certify that the dissertation entitled “OOxxiiddaattiioonn ooff AAllccoohhooll CCoommppoonneenntt ooff
MMiiccrrooeemmuullssiioonn BByy LLiippoopphhyylliicc CCrr((VVii))” being submitted by Mr. Santosh Kumar
Behera to the Department Of Chemistry, National Institute Of Technology, Rourkela-
769008, for the award of the degree of Master Of Science in Chemistry, is a record of
bonafide research carried out by him under my supervision and guidance. The
dissertation report has reached the standard fulfilling the requirements of the
regulations relating to the nature of the degree.
I further certify that to the best of my knowledge Mr. Behera bears a good moral
character.
NIT-Rourkela
Date:
Sabita Patel
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ACKNOWLEDGEMENT
I owe this unique opportunity to place on record my deep sense of gratitude &
indebtedness to Dr. SABITA PATEL, Asst.Professor, CHEMISTRY Department, NIT,
Rourkela for his scholastic guidance, prudent suggestions & persistent endeavor throughout
the course of investigation.
I owe a deep sense of reverence to Prof. B.G.MISHRA, HOD, of chemistry, NIT,
Rourkela, for giving me the opportunity to do the project work in the institute
My sincere gratitude is to Sarita Garanayak for her overall guidance, immense help,
valuable suggestions, constructive criticism & painstaking efforts in doing the experimental
work & preparing the thesis.
I express my profound gratitude to Mr.Prakash Kumar Malik, Subhasis, and
Shailesh for their ceaseless encouragement, immense help, and hearty encouragement during
my project work.
I wish to thank all the research scholar of Organic lab, NIT for help and support during
the present study..
Lastly I express my abysmal adoration & heartfelt devotion to my beloved parents
for their countless blessings, unmatchable love, affection & incessant inspiration that has
given me strength to fight all odds & shaped my life, career till today.
In the end I must record my special appreciation to GOD who has always been a
source of my strength, inspiration & my achievements.
Name: Santosh Kumar Behera
Date: 05.05.2011
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CONTENTS
1. Introduction and literature review
2. Experimental
3. Results and Discussion
4. Conclusion
5. References
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1. INTRODUCTION AND LITERATURE REVIEW
The concept of microemulsion was first introduced by Hoar and Schulman in 1943.1
They prepared the first microemulsions by dispersing oil in an aqueous surfactant
solution and adding an alcohol as a co-surfactant, leading to a transparent, stable
formulation. “A microemulsion is a system of water, oil, and amphiphilic compounds
(surfactant and co-surfactant) which is a transparent, single optically isotropic, and
thermodynamically stable liquid”. Microemulsions are formed when and only when
(i) the interfacial tension at the oil/water interface is brought to a very low level and
(ii) the interfacial layer is kept highly flexible and fluid.2 These two conditions are
usually met by a careful and precise choice of the components and of their respective
proportions, and by the use of a “co-surfactant” which brings flexibility to the
oil/water interface.2
These systems are currently of interest due to its application in the following fields.3
Microemulsions in enhanced oil recovery.
Microemulsions as fuels
Microemulsions as lubricants, cutting oils and
corrosion inhibitors
Microemulsions as coatings and textile finishing
Microemulsions in detergency
Microemulsions in cosmetics
Microemulsions in agrochemicals
Microemulsions in food
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Microemulsion in pharmaceuticals as drug delivery systems
Microemulsions in environmental remediation and
Detoxification
Microemulsions in analytical applications
Microporous media synthesis (microemulsion gel technique)
Microemulsions as liquid membranes
Microemulsions in biotechnology
Furthermore microemulsions are gentle solvents for extraction of proteins without
altering their enzymatic or functional properties although the process can readily be
scaled by conventional liquid–liquid extraction techniques. Therefore this can also be
used for bioseparations.
Due to varied consistencies and microstructures, microemulsions have been used as a
reaction media for a variety of chemical reactions such as synthesis of nanoparticles,4
polymerization,5,6,7
photochemical, electrochemical and electrocatalytic and organic
synthesis.
Zhou et al.8 have investigated the bicontinuous microemulsions made from dodecane,
water, and didodecyldimethylammonium bromide (DDAB) as media for the catalytic
reduction of trans- 1,2-dibromocyclohexane (DBCH) and for SN2 reactions of n-alkyl
bromides with electrochemically generated Co(1) complexes. Macrocyclic complexes
vitamin B 12 (a cobalt corrin) and Co(salen) resided in the water phase, while the
alkyl bromides resided in the oil phase of the microemulsion. Rates of DBCH
reduction is 40-fold larger in the bicontinuous fluid than in a water-in-oil
microemulsion which is attributed to the larger interfacial area of the bicontinuous
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system. Formal potentials in the microemulsion depended on specific interactions,
such as those of [Col(salen)]- with cationic surfactant head groups or the influence of
water phase pH on vitamin B12.
Shrikhandea et al.9
have studied the condensation between benzaldehyde and acetone
in a cationic o/w microemulsion prepared from the combination of n-butanol as co-
surfactant, n-hexane as oil and cetyltrimethylammonium bromide (CTAB) as the
cationic surfactant (Scheme 1). They have also determined the hydrodynamic
diameters of the oil droplets in the o/w microemulsion at different compositions using
dynamic light scattering. Various parameters influencing the formation of
microemulsions, like oil content, surfactant content, oil and co-surfactant ratio were
varied and their corresponding effects on the solubilization of reactants and rate of a
condensation reaction were studied. A direct correlation between the droplet size of
the microemulsion and rate of the reaction is observed. The changes in solubility of
benzaldehyde in the microemulsion affect the reaction rate while the composition of
the oil phase does not influence the rate of the reaction.
Scheme-1
From this study they have concluded the that, the solubilization capacity of
benzaldehyde is decreased with the increase in oil + co-surfactant and the surfactant
content, indicating that the aldehyde is solubilized at the interface rather than the core
of the droplet. Further from the decrease in observed reaction rate constants on
variation in oil + co-surfactant and surfactant content further indicate that the reaction
takes place at the interface.
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The atmospheric and electrochemical oxidation of AA(Ascorbic acid) in the SDS
micellar solutions and in the microemulsions pentanol/water stabilized by SDS have
been studied by Szymul et al.10
(Scheme-2). They found that the hydrophilic vitamin
C readily dissolves in water and O/W microemulsions as well as undergoes the
irreversible two-electron oxidation reaction and the atmospheric oxidation of AA is
accelerated by the SDS up to the CMC and inhibited in the concentrated SDS
solutions. They also found that the rate of atmospheric oxidation of ascorbic acid is
higher in the water-in-oil (W/O) than in the oil-in-water (O/W) microemulsions and
increases with the increasing oil content. The influence of the SDS on the
electrochemical behavior of vitamin C was also studied. The general conclusion
emerging from this investigation is that the increasing surfactant concentration shifts
the ascorbic acid oxidation potential to higher values whereas the corresponding peak
current values diminish. In the microemulsions the AA oxidation is slowed down by
increasing the pentanol amount in the system.
The oxidation reaction of L-ascorbic acid
Sathishkumar et al11
were synthesized n-Hexyl- -d-glucopyranoside (HGP) through
the -glucosidase-catalyzed condensation of glucose and hexanol in an aqueous-
organic bicontinuous microemulsion system with both water and oil as continuous
Scheme-2
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phases. Methodology for separation of HGP from the microemulsion system for
analysis by gas chromatography was developed. Various factors influencing the
synthesis of HGP like reaction time, enzyme concentration and temperature were
optimized experimentally. Reverse reaction (hydrolysis) occurred was also studied.
Comparison of the rate of the reaction between synthesis and hydrolysis showed the
latter to be faster, suggesting that bicontinuous microemulsion system is more
applicable to the enzymatic hydrolysis. Degradation of enzyme in bicontinuous
microemulsion system was very negligible.
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2. EXPERIMENTAL
Synthesis of Cetyltrimethylammonium dichromate (CTADC)
CTADC was prepared (Scheme-1) by adding aqueous solution of K2Cr2O7 (0.037mol)
in small portions to the flask containing aqueous solution of cetyltrimethylammonium
bromide (CTAB) (0.2mol) with stirring.Yellow precipitate appeared immediately. It
was filtered, washed properly till the filtrate in free from trace of dichromate and
bromide. It was dried and kept in sample bottle.
The prepared yellow solid was characterized using CHN, IR and NMR analytical data.
M.Pt. 212 oC, yield: 98%.Elemental analysis: C,58.14; H, 10.65; N, 3.54; Cr, 13.11.
C38H84O7N2Cr2 requires C, 58.16; H, 10.71; N, 3.57; Cr, 13.26. IR (cm_1): 771,
879, 933, 1467, 2850, 2921, 3028, 3471. NMR (CDCl3, 300MHz): d 0.86 (t, 6H),
1.29 (m, 48H), 1.67 (m, 4H), 1.74 (m, 4H), 3.42 (s, 18H), 3.51 (m, 4H) (Scheme-3).
N
CH3
CH3
CH3
K2Cr2O7Br-
CTAB
N
CH3
CH3
CH3
Cr2O7--
2
CTADC
(Scheme 3)
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Oxidation of Butanol by CTADC
Different microemulsions were prepared using Surfactant(TX-100,CTAB and
SDS),Cosurfactant (n-Butanol),Oil(Chloroform),Water in Acetic acid medium. Phase
diagrams were drawn for different systems. The microemulsions are used to study the
oxidation of alcohol by CTADC at varying concentrations of oxidant, butanol,
surfactant, acid etc to unveil the reaction mechanism in this medium. The product was
found to be butanal.
The kinetics of the oxidation reaction was studied using UV-Vis spectrophotometer by
monitoring the change in absorbance of CTADC at 350 nm. Pseudo first order
condition was maintained throughout the experiment. The observed rate constant kobs
was calculated using 1st order rate expression as follows.
Where OD0 , ODt, OD and t refers to optical density of CTADC at 350 nm before the
commencement of the reaction, optical density at any time t, optical density at infinite
time or after completion of the reaction and reaction time respectively. A
representative time scan spectra is given in figure. 1.
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Figure 1: representative UV-Vis time scan plot for the oxidation of butanol by
CTADC in microemulsion medium
0
0.1
0.2
0.3
0.4
0.5
0.6
300 350 400 450 500 550
Ab
sorb
ance
Wave length in nm
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3. RESULTS AND DISCUSSION
Cr(VI) is known for its versatility the oxidation reaction. It can oxidise a variety of
substrates alkane, alcohol, aldehyde, thiols etc. For the oxidation process it generally
requires a high concentration of concentrated sulphuric acid. For which it is very
difficult to undertake reactions in milder conditions for acid sensitive compounds.
Further the insolubility of potassium dichromate in non-aqueous solvents makes the
oxidation process difficult and tedious for water insoluble organic substrates. To
overcome these difficulties different Cr(VI) oxidants are explored with counter ions
like ammonim, phosphonium etc.
An onium ion, as the counterion for anionic oxidants, makes a lot of difference in
oxidation potential of the oxidant as well as to the oxidizing system.12
A large number
of Cr(VI) oxidants with onium ions have been reported. 12
In a continuation of our efforts to explore some biomimetic oxidants to oxidize
organic substrates in organic solvents, we have reported the oxidation behavior of
cetyltrimethylammonium dichromate (CTADC) toward various organic substrates.
This reagent is water insoluble and stable at room temperature for more than a year
when kept in sealed bottle. It absorbs around 353-383 nm. Exists as a tight ionpair and
forms monolayer on water surface with area/molecule 51 Å2.13
Although Cr(VI) is
undisputedly carcinogenic, the insolubility in water reduces contamination of Cr(VI)
in aqueous medium, and the compound thus can be used as a green reagent. Further,
CTADC is devoid of an acidic proton and thus is relatively milder than other Cr(VI)
oxidants. In the absence of acid, CTADC exhibits some bizarre reactions with
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nonconventional products. Aromatic amines are found to yield corresponding diazo
compounds,14
and arylaldoximes yielded corresponding nitriles.15
In an oxidation reaction of cholesterol with CTADC, Patel et al.16
have observed that
7-dehydrocholesterol is obtained instead of usual product cholestenone. This
dehydrogenation is a rare event in Cr(VI) oxidation studies, and it is explained
through remote functionalization mechanism where the cetyltrimethylammonium ion
provides a favourable environment for proper orientation of the dichromate group so
that the removal of hydrogen from 7th
and 8th
position becomes easier.
Owing to the applicability of CTADC as biomimetic oxidant, present project aims at
the oxidation of different substrates in microemulsion medium which is mimicking the
cell structure. We have chosen butanol as the substrates for the oxidation process.
Oxidation of alcohol by CTADC in nonaqueous medium has benn studied extensively
by Patel and Mishra17
. A Michaelis- Menten type kinetics was reported by them with
change in substrate concentration (Figure 2). From the dependence of rate with
various factor and order with respect to all the reactants the following rate expression
(eq 3) and mechanism has been proposed (Scheme 4).
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1
][
11
kAlcoholKkkobs
(3)
15
(Scheme 4)
Figure 2
To study the oxidation reaction in microemulsion medium, we have constructed the
phase diagrams with varying concentration of the components (Figure 8). In all the
phase diagrams chloroform is used as oil phase because of the solubility of CTADC in
chloroform. The surfactants used are Triton X-100 (TX100) a non-ionic surfactant,
Cetyltrimethylammonium bromide (CTAB) a cationic surfactant and sodium
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dodecylsulphate (SDS) an anionic surfactant with different composition with the
cosurfactant n-butanol. Acetic acid is used as catalyst for the oxidation process.
CTAB: nBuOH(1:6.5),Chloroform,Water CTAB: nBuOH (1:6.5), Chloroform,CTADC,Water
SDS:nBuOH(3:1),Chloroform,Water
SDS:nBuOH(3:1),Chloroform,Water
Fig-3a Fig-3b
Fig-3c Fig-3d
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Figure 3 (a-i): represents the Pseudo-ternary phase diagram of the microemulsion
system at different S/CS ratios. E, W and O in all the plots represents 100%
emulsifier, 100% water and 100% oil respectively. The shaded regions in the diagrams
represent turbid zone and the rests are clear domain.
From these pseudoternary phase diagram it is seen that microemulsion in presence of
CTAB have less clear region than that of the anionic surfactant such as SDS. In SDS
microemulsion the clear region that is the Winsor-IV domain is larger in presence of
SDS:nBuOH(3:1),Chloroform,CTADC,AcOH,Water
TX-100:BuOH(1:4),Chloroform,Water
TX-100:nBuOH(1:4),Chloroform,CTADC,Water
TX-100:nBuOH(1:4),Chloroform,CTADC,AcOH
Fig-3f
Fig-3i Fig-3h
Fig-3g
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CTADC.This may be due to the participation of CTADC as surfactant in the
formation of isotropic microemulsion.
The oxidation of CTADC in various microemulsion medium can be determined by
monitoring the depletion of the CTADC at 350 nm. The observed rate constants are
tabulated in Table 1.
Table 1: Change in kobs with Variation of TX-100 concentration for the oxidation
of butanol by CTADC in microemulsion.[CTADC]=5 X 10-5
[Butanol]=1.8 X 10-
1[Acetic acid]=1.45 X 10
-1Temp= 25
oC.
SL.NO. [TX-100] 103 (mol) kobs x10
4 (sec
-1)
1 6.0 6.1
2 12.12 6.5
3 18.2 6.7
4 24.26 8.1
5 30.32 9.6
From the table it is clear that with increase in surfactant concentration rate constant
increases, hence rate increases. This may be attributed to the higher solubility of
CTADC and n-butanol in micellar region which increases the amount of reactants in
close proximity which in turn increases the rate of the reaction.
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Table 2: Change in kobs with Variation of CTADC concentration for the oxidation of
butanol by CTADC in microemulsion. [Butanol]= 1.8 X 10-1
, [Acetic acid]= 1.45 X 10-1
, Temp. = 25 oC
SL.NO. [CTADC] x 105(mol) Kobs x 10
4(sec
-1)
1 0.83 3.6
2 1.66 4.9
3 3.33 5.5
4 5.0 5.6
Figure 4: Plot of Log (rate) vs. Log[CTADC] for the oxidation of butanol in
microemulsion formed by TX 100.
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Table 3: Change in kobs with Variation of Acetic acid concentration for the
oxidation of butanol by CTADC in microemulsion.[CTADC]= 2 X 10-5
,
[Butanol]= 1.8 X 10-1
,[Acetic acid]= 1.45 X 10-1
Temp.= 25 oC.
SL.NO. [AcOH] x 101(mol)
kobs x 10
4 (sec
-1)
1 3.5 4.0
2 6.72 7.2
3 10.11 8.4
4 12.9 12.3
5 15.88 23.4
From this data in table 4 it is seen that with increase in CTADC concentration rate of
the reaction increases. From the plot of log[rate] vs. log[CTADC] (figure 4) the order
with respect to CTADC is found to be 1. With increase in acetic acid concentration the
rate increases with an uncatalytic rate 1.1 x 10-4
.
Table 4: Change in kobs with Variation of butanol concentration for the oxidation
of butanol by CTADC in microemulsion. [CTADC]= 2.5 X 10-5
[Acetic acid]=
1.45 X 10-1
,Temp.= 25 oC
SL.NO. [Butanol] x 105 (mol) Kobs x 10
4(sec
-1)
1 3.64 9.6
2 7.28 11.5
3 10.92 23.0
4 14.57 38.38
5 18.2 22.03
6 21.85 8.1
7 25.5 6.9
8 29.13 5.8
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Figure5: Plot of kobs versus [n-butanol] in the oxidation of butanol by CTADC in
microemulsion medium.
With increase in butanol concentration in the mixture, the rate of a reaction increases
up to the concentration of 14.57 x 10-4
of butanol then it sharply decreases (figure.5).
This may be attributed to the structural change accompanied at higher concentration of
butanol. As the n-butanol concentration increases in the micellar interface, replaces
the CTADC. CTADC gets penetrated towards the micellar core as the solubility is
higher in the non-polar medium. So the availability of CTADC in the interface region
decreases. Hence protonation of H+ with dichromate ion decreases. At higher butanol
concentration, due to the increase partition of the reactants H+, CTADC and n -
butanol in different medium the rate of the reaction decreases.This phenomenon is
shown in the following figure. 6.
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Figure 6: Schematic representation of partition of butanol and CTADC in
microemulsion with increase in butanol content
4. Conclusion
Oxidation of butanol in microemulsion by CTADC (Lipophylic oxidation) has been
undertaken. The reaction is 1st order with respect to the oxidant CTADC. With increase in
surfactant concentration and acid concentration rate of the reaction increase.With increase in
n-Butanol concentration rate increases up to 15x10-2
M and the order with respect to butanol
is found to be1. After 15x10-2
M concentration of n-butanol rate decreases due to structural
change.
23
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